1. Technical Field
This invention relates to the control of computer-aided machine tools, and more particularly an NC machining simulation system using a non-manifold data structure.
2. Description of the Prior Art
In machining parts by using an NC machine tool, it is necessary to select a curve on which to move the tool three-dimensionally. Hence, it is rather common for a machining designer to make corrections by repeating computer-aided simulation in the phase of tool path design prior to actual machining while running visual checks as to whether the final shape intended can be obtained, whether or not the cutting edge stays in stable contact with a shape to be cut during machining, whether or not there are redundant tool paths, and so on.
Machining simulation is largely divided into two types, i.e., geometrical simulation that evaluates changes in the shape of a workpiece with the travelling of a tool, and physical simulation that evaluates physical quantities such as cutting force, vibration, and heat varying in the course of machining. This invention deals chiefly with the former.
The geometrical simulation of machining employs a method in which the volume to be cut away by the intervention of the tool are deducted sequentially from a model in the original shape (unmachined shape) programmed into a computer beforehand by performing Boolean operations on the solid. Conventionally, these Boolean operations used to be performed on a boundary representation model, or what is called a solid model. However, this technique had restrictions in that only the surfacial shape of a workpiece is obtained as a result of the simulation. Therefore, one must employ either (a) or (b) below if it is desired to check for time-serial changes in the shape:
(a) to observe gradual transformations of the model in question with the progress of computation PA1 (b) to copy onto another shape model as many transformations of the original shape as necessary during the actual process PA1 redoing a series of Boolean operations beginning with the original shape PA1 performing reverse-Euler operations to reverse the steps where a series of Boolean operations were modified after recording the model transformational operations performed during the Boolean operations by performing Euler operations
Method (a), on the one hand, takes too much time because the conventional technique allows data about in-process shapes to exist only at particular intermediate points of time in the course of Boolean operations and necessitates the performing of numerous Boolean operations, thus entailing a heavy workload in order to observe the progress of machining with precision. Method (b), on the other hand, necessitates the preparation of many copies of data, resulting in the disadvantage of massive data accumulation.
Moreover, in order to make even a partial change in the machining procedure or tool paths in reference to a simulation result, the conventional method entails either:
or
(An Euler operation is a transformational operation such that the expression v-e+f=2 (s-h)+r holds true where v=number of vertexes, e=number of edge lines, f=number of surfaces, s=number of connected components, h=number of through holes, and r=number of surfacial holes. For details, refer to H. Chiyokura, "Solid Modeling with Design Base," Addison-Wesley, 1988, for example.)
However, both methods entail performing repeated Boolean operations and thus consume much in computation costs. Again, the more complex the machining process of parts is, the longer the time required for recomputation becomes.
PUPA 63-271578 deals with Boolean operations on three-dimensional bodies and related display methods for the simulation of the behavior of NC machine tools, and discloses that inputting a plurality of data elements defining a three-dimensional finite domain within three-dimensional finite space, dividing the fine space sequentially into segments until the data comes to meet particular conditions determined by a combination of data conditions representing a domain with an empty part and real part and conditions of data representing a real domain, generating data defining each of those segmented domains, and achieving Boolean operations on those two or more domains through performing Boolean operations on the data defining said segmented domains.
PUPA 1-292474 discloses the provision of an intersection detecting means for detecting mutual contact between the facets, edge lines, and vertexes of two solids in a three-dimensional solid interference arithmetic units for constructing solids by using Boolean operations and a coordinate shifting means for shifting the coordinates of facets, edge lines, and vertexes in directions in which the solids may expand or contract when some contact is detected by the intersection detecting means.
However, these techniques of the prior art do not provide processing efficiency high enough to facilitate the interactive designing/editing of tool paths.
PUPA 2-132573, with which this applicant is concerned here, does not necessarily enlighten us on the application of a boundary representation solid model using a non-manifold data structure to NC machining simulation, although it discloses such a system and hence provides a background technology for this invention.
The object of this invention is to enable machining simulation based on estimated tool paths to be carried out interactively at high efficiency in designing/editing tool paths for NC machine tools.